Catheter with tissue protecting assembly

ABSTRACT

A medical probe includes an elongate member having a proximal end and a distal end, an ablative element mounted to the distal end of the elongate member, and a cage assembly mounted to the distal end of the elongate member, the cage assembly at least partially covers the ablative element. A method of treating tissue in a body includes inserting an ablative element in the body, placing the ablative element adjacent the tissue, and maintaining a distance between the ablative element and the tissue using a protective catheter element that circumscribes at least a portion of the ablative element.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/499,650, filed Jul. 8, 2009, now U.S. Pat. No. 8,221,407, which is acontinuation of U.S. application Ser. No. 10/660,820, filed Sep. 12,2003, now U.S. Pat. No. 7,569,052; the entire disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention pertains to devices and methods for ablation oftissue, and more particularly, to ablation devices and methods forcreating lesions within internal body organs, such as the heart.

BACKGROUND

Physicians make use of catheters today in medical procedures to gainaccess into interior regions of the body to ablate targeted tissueareas. For example, in electrophysiological therapy, ablation is used totreat cardiac rhythm disturbances. During these procedures, a physiciansteers a catheter through a main vein or artery into the interior regionof the heart that is to be treated. The physician places an ablatingelement carried on the catheter near the targeted cardiac tissue, anddirects energy from the ablating element to ablate the tissue and form alesion. Such procedure may be used to treat arrhythmia, a condition inthe heart in which abnormal electrical signals are generated in theheart tissue.

In certain procedures, it may be desirable to produce a deep lesion. Forexample, it may be desirable to produce a transmural lesion (lesion thatextends the depth of a tissue) within ventricle tissue, because shallowor incomplete lesions may otherwise allow electrical signals to travelthrough the non-ablated tissue beneath the lesion. Therefore, it isbelieved that deep or transmural lesions can more efficiently blockundesirable electrical paths. Because the ventricle tissue is thick,however, it may be difficult to create transmural lesions using thecurrent technology.

An ablation procedure using a unipolar arrangement involves placing anindifferent patch electrode or a ground pad on a patient skin. Ablationenergy is directed from another electrode (the ablating electrode)placed against the target tissue, while the indifferent patch electrodeis electrically coupled to a ground or return input on theradio-frequency generator, thereby completing the energy path. In thiscase, ablation energy will flow from the ablating electrode to the patchelectrode. One of the disadvantages of this procedure is that much ofthe RF energy is dissipated or lost through intervening organs, tissues,and/or blood pool between the ground pad and the target tissue that isbeing ablated. As the result, it is more difficult to ablate tissuebelow the surface of the target site using current unipolararrangements.

An ablation procedure using a bipolar arrangement involves using anablation catheter that carries two electrodes. In this case, ablationenergy will flow from one electrode (the ablating electrode) on thecatheter to an adjacent electrode (the indifferent electrode) on thesame catheter. Because both the ablating electrode and the indifferentelectrode are usually located on one side of the tissue to be ablated,some of the ablation energy delivered by the ablating electrode may onlyaffect tissue that is closer to the surface of the target site, and maytend to return to the indifferent electrode without substantiallyaffecting deeper tissue. As a result, it is more difficult to ablatetissue below the surface of the target site using current bipolararrangements.

Another problem associated with current ablation devices is that duringan ablation procedure, a return electrode used for returning energy toan ablation source may heat up. In the unipolar arrangement where thereturn electrode is placed in contact with a patient's skin, theoverheating of the return electrode may cause injury to the patient'sskin. In the bipolar arrangement where the return electrode is placedwithin the body and adjacent to the ablating electrode, the overheatingof the return electrode may cause internal healthy tissue that is incontact with the return electrode to be unnecessarily heated.

Furthermore, ablation of heart tissue poses another challenge in thatthe heart is constantly moving during an ablation procedure. As aresult, it is difficult to maintain stable contact between an ablatingor ground electrode and the constantly moving target tissue.

Thus, there is currently a need for an improved ablation device andmethod for creating lesions.

SUMMARY OF THE INVENTION

A medical probe includes an elongate member having a proximal end and adistal end, an ablative element mounted to the distal end of theelongate member, and a cage assembly mounted to the distal end of theelongate member. The cage assembly at least partially covers theablative element and prevents the ablative element from directlycontacting and damaging a healthy tissue due to overheating of theablative element during use. By means of non-limiting example, the cageassembly may include a distal end, a proximal end, and a plurality ofstruts secured between the distal and proximal ends. The cage assemblymay also be made from a woven or braided structure.

A method of treating tissue in a body includes inserting an ablativeelement in the body, placing the ablative element adjacent the tissue,and maintaining a distance between the ablative element and the tissueusing a protective catheter element that circumscribes at least aportion of the ablative element.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the drawings, whichis intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are illustrated by way ofexample, and not by way of limitation, in the figures of theaccompanying drawings, in which like reference numerals refer to likecomponents, and in which:

FIG. 1 is a block diagram of an ablation system constructed inaccordance with one embodiment of the present invention;

FIG. 2A is a perspective view of an embodiment of a cannula that may beused with the system of FIG. 1;

FIG. 2B is a perspective view of an alternative embodiment of a cannulathat may be used with the system of FIG. 1;

FIG. 2C is a cross-sectional view of an alternative embodiment of thecannula of FIG. 2A or 2B;

FIG. 3 is a plan view of an embodiment of an ablation catheter that maybe used with the system of FIG. 1;

FIG. 4 is a cross-sectional view of an embodiment of an electrodestructure and stabilizer used in the ablation catheter of FIG. 3,particularly showing the electrode structure in a deployedconfiguration;

FIG. 5 is a cross-sectional view of the electrode structure of FIG. 4,particularly showing the electrode structure in an undeployedconfiguration;

FIG. 6 is a cross-sectional view of an alternative embodiment of anablation catheter that may be used with the system of FIG. 1;

FIG. 7 is a cross-sectional view of a variation of the ablation catheterof FIG. 6;

FIG. 8 is a partial cut-away view of an alternative embodiment of anelectrode structure that can be used in the ablation catheter of FIG. 3;

FIG. 9 is a cross-sectional view of the electrode structure of FIG. 8;

FIG. 10 is a partial cut-away view of still another alternativeembodiment of the electrode structure of FIG. 3;

FIG. 11A is a partial cut-away view of yet another alternativeembodiment of an electrode structure that can be used in the ablationcatheter of FIG. 3;

FIG. 11B is a partial cut-away view of yet another alternativeembodiment of an electrode structure that can be used in the ablationcatheter of FIG. 3;

FIG. 11C is a partial cut-away view of yet another alternativeembodiment of an electrode structure that can be used in the ablationcatheter of FIG. 3;

FIG. 12 is a partial side cross-sectional view of the electrodestructure of FIG. 11A, showing the RF wire embedded with the wall of thebody;

FIG. 13 is a partial side cross-sectional view of the electrodestructure of FIG. 11A, showing the RF wire carried within the interiorof the body;

FIG. 14 is a cross-sectional view of an embodiment of the electrodestructure and stabilizer of FIG. 3, showing the details of thestabilizer;

FIG. 15 is a top view of the electrode structure of FIG. 14;

FIG. 16 is a cross-sectional view of a variation of the stabilizer ofFIG. 14;

FIG. 17 is a top view of an alternative embodiment of the stabilizer ofFIG. 3;

FIG. 18 is a cross-sectional view of another embodiment of the electrodestructure of FIG. 3, showing the stabilizer internal to the body;

FIG. 19A shows another embodiment of an ablation catheter that may beused with the system of FIG. 1;

FIG. 19B is a cross-sectional view of another embodiment of an ablationcatheter that may be used with the system of FIG. 1;

FIG. 20 is a top view of an embodiment of a ground probe that may beused with the system of FIG. 1;

FIG. 21 is a partial side view of the ground probe of FIG. 20, showingthe distal region of the sleeve folded within a body lumen;

FIG. 22 is a partial side view of another embodiment of the ground probeof FIG. 20, showing the ground probe having a cage assembly;

FIG. 23 is a partial side view of the ground probe of FIG. 22, showingthe cage assembly having a collapsed configuration;

FIG. 24 is a partial side view of an alternative embodiment of a groundprobe that may be used with the system of FIG. 1;

FIG. 25 is a partial side view of the distal region of the ground probeof FIG. 24, showing the sleeve advanced from the sheath to form a loop;

FIG. 26 is a partial side view of an alternative embodiment of theground probe of FIG. 24, showing the spring member secured to theexterior of the sheath;

FIG. 27A is a perspective view of an embodiment of a mapping catheterthat may be used with the system of FIG. 1;

FIG. 27B is a perspective view of the mapping catheter of FIG. 27A;

FIG. 28A is a perspective view of another embodiment of a mappingcatheter that may be used with the system of FIG. 1;

FIG. 28B is a perspective view of the mapping catheter of FIG. 28A;

FIG. 29A is a perspective view of another embodiment of a mappingcatheter that may be used with the system of FIG. 1;

FIG. 29B is a perspective view of the mapping catheter of FIG. 29A;

FIGS. 30A-30D are diagrams showing a method of using the system of FIG.1 to create a transmural lesion at the right ventricle of a heart;

FIG. 31 shows, in diagrammatic form, anatomic landmarks for lesionformation in left and right atriums;

FIGS. 32A and 32B show representative lesion patterns in a left atriumthat may be formed using the system of FIG. 1; and

FIG. 33A-33C show representative lesion patterns in a right atrium thatmay be formed using the system of FIG. 1.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Various embodiments of the present invention are described hereinafterwith reference to the figures. It should be noted that the figures arenot drawn to scale and that elements of similar structures or functionsare represented by like reference numerals throughout the figures. Itshould also be noted that the figures are only intended to facilitatethe description of specific embodiments of the invention. They are notintended as an exhaustive description of the invention or as alimitation on the scope of the invention. In addition, an illustratedembodiment needs not have all the aspects or advantages of the inventionshown. An aspect or an advantage described in conjunction with aparticular embodiment of the present invention is not necessarilylimited to that embodiment and can be practiced in any other embodimentsof the present invention even if not so illustrated.

Referring to FIG. 1, a tissue ablation system 100 constructed inaccordance with one embodiment of the present invention is shown. Thesystem 100 comprises an imaging cannula assembly 102, which includes acannula 201, an imaging device 214 (e.g., a charge coupled device (CCD)camera) that provides imaging functionality to the cannula 201, and alight source 220 that provides optical viewing functionality to thecannula 201. The imaging cannula assembly 102 is configured to bepartially inserted through a patient's skin in order to provide accessto, and imaging of, a target area on the exterior surface of an organ,such as a heart.

The system 100 further comprises an ablation assembly 105, whichincludes an ablation catheter 104, a pump 409 for providing an inflationmedium to the ablation catheter 104, a vacuum 598 that providesstabilizing functionality to the ablation catheter 104, a groundcatheter 106, and an ablation source 108. The ablation catheter 104 isconfigured to be introduced to a target area facilitated by the cannulaassembly 102, and the ground catheter 106 is configured to beintravenously introduced within an organ. The ablation catheter 104 andthe ground catheter 106 are electrically coupled to the respectivepositive and negative terminals (not shown) of the ablation source 108,which is used for delivering ablation energy to the ablation catheter104 to ablate target tissue during use. The ablation source 108 ispreferably a radio frequency (RF) generator, such as the EPT-1000 XPgenerator available at EP Technologies, Inc., San Jose, Calif.

The system 100 also includes a mapping catheter 700 for sensing anelectric signal at a heart and a mapping processor 730 that analyzessensed signals or data from the catheter 700 to thereby determine atarget site to be ablated, and a vacuum 732 that provides stabilizingfunctionality to the mapping catheter 700.

The Cannula

Referring now to FIG. 2, the details of the cannula 201 will bedescribed. The cannula 201 includes a shaft 202 having a proximal end204, a distal end 206, and a lumen 208 extending between the proximalend 204 and the distal end 206. In the illustrated embodiment, the shaft202 has a circular cross-sectional shape and a cross-sectional dimensionthat is between 0.25 to 1.5 inches. However, the shaft 202 may also haveother cross-sectional shapes and dimensions. As shown in FIG. 2A, thedistal end 206 of the shaft 202 has a substantially pre-shapedrectilinear geometry. Alternatively, the distal end 206 may have apre-shaped curvilinear geometry (FIG. 2B), which may be used to guidethe ablation catheter 104 away from a longitudinal axis 211 of the shaft202.

The shaft 202 is made of, for example, a polymeric, electricallynonconductive material, like polyethylene, polyurethane, or PEBAX®material (polyurethane and nylon). Alternatively, the shaft 202 is madefrom a malleable material, such as stainless steel or aluminum, therebyallowing a physician to change the shape of the shaft 202 before orduring an operation. Even more alternatively, the distal end 206 is madesofter than the proximal portion of the cannula 201 by using differentmaterial and/or having a thinner wall thickness. This has the benefit ofreducing the risk of injury to tissue that the distal end 206 may comein contact with during an operation. The cannula 201 also includes aliner 209 composed of a suitable low friction material, e.g., TEFLON®,Polyetheretherketone (PEEK), polyimide, nylon, polyethylene, or otherlubricious polymer linings, to reduce surface friction with the ablationcatheter 104 as it slides within the lumen 208.

The cannula 201 also includes an imaging window 210 located at thedistal end 206 of the shaft 202, and an imaging cable 216 housed withina wall 222 of the cannula 201. The imaging cable 216 couples the imagingdevice 214 to the imaging window 210, so that the cannula 201 is capableof sensing images in the vicinity of the distal end 206 of the shaft202. The cannula 201 further includes one or more optical windows 212(in this case, two) located at the distal end 206 of the shaft 202, andfiber-optic cables 218 housed within the wall 222 of the cannula shaft202. The fiber-optic cables 218 couple the light source 220 to theoptical windows 212, so that the cannula 201 is capable of supplyinglight to illuminate objects that are being imaged.

The cannula 201 optionally includes a stopper 224 slidably secured tothe surface of the shaft 202. The stopper 224 includes an opening 226through which the shaft 202 can slide, and a locking mechanism 228 forsecuring the stopper 224 to the shaft 202 during use of the cannula 201.In the illustrated embodiment, the locking mechanism 228 includes ascrew that can be screwed through a wall of the stopper 224 intoengagement with the outer surface of the cannula shaft 202. In analternative embodiment, the opening 226 of the stopper 224 can have across-sectional dimension equal to a cross-sectional dimension of theshaft 202 to provide a frictional engagement between the stopper 224 andthe shaft 202. Other securing mechanisms may also be used. In anotheralternative embodiment, the stopper 224 may be fabricated together withthe shaft 202 as one unit. In any event, the stopper 224 is configuredfor bearing against a trocar (not shown) secured to a patient's skinduring an operation. Alternatively, the stopper 224 can be configured todirectly bear against a patient's skin.

As shown in FIG. 2C, in another embodiment, the cannula 201 furtherincludes one or more dividers 221 (in this case, one) for separating thelumen 208 into two or more compartments. Such configuration allows morethan one device, such as a catheter, probe, scissor, clamp, and forceps,to be inserted into a patient through the cannula shaft 202, while theother compartment carries a catheter, such as the ablation catheter 106or the mapping catheter 700.

The Ablation Catheter

Turning now to FIG. 3, the details of the ablation catheter 104 will bedescribed. The ablation catheter 104 includes an actuating sheath 300having a lumen 301, and a catheter member 302 slidably disposed withinthe lumen 301 of the sheath 300. The ablation catheter 104 furtherincludes an electrode structure 310 for transmitting ablation energy toadjacent tissue, and a vacuum actuated stabilizer 400 mounted to thedistal end 306 of the catheter member 302 for stabilizing the electrodestructure 310 relative to the tissue. The ablation catheter 104 furtherincludes a handle assembly 320 mounted to the proximal end 304 of thecatheter member 302. The handle assembly 320 includes a handle 321 forproviding a means for the physician to manipulate the ablation catheter104, and an electrical connector 362 coupled to the ablation source 108for providing ablation energy to the electrode structure 310. The handleassembly 320 further includes a vacuum port 408 coupled to the vacuum598 for generating a vacuum force for the stabilizer 400, and aninflation port 336 coupled to the pump 409 for supplying the electrodestructure 310 with pressurized inflation medium.

The sheath 300 and the catheter member 302 are preferably made from athermoplastic material, such as a polyurethane, a polyolefin orpolyetherpolyamide block copolymer. In an alternative embodiment, thecatheter member 302 is composed of an extrusion of wire braided plasticmaterial and a flexible spring that is disposed within the extrudedmaterial.

The handle assembly 320 includes a steering mechanism 500 for steeringthe electrode structure 310. The steering mechanism 500 includes asteering lever 502 operable for steering of the electrode structure 310.The steering mechanism 500 further includes a locking lever 504 operablein a first position to lock the steering lever 502 in place, and in asecond position to release the steering lever 502 from a lockedconfiguration. Further details regarding this and other types of handleassemblies can be found in U.S. Pat. Nos. 5,254,088, and 6,485,455 B1,the entire disclosures of which are hereby expressly incorporated byreference.

The electrode structure 310 can be variously constructed. For example,FIGS. 4 and 5 illustrated one embodiment of an electrode structure310(1). The electrode structure 310(1) includes anexpandable-collapsible electrode body 330, which can be altered betweenan enlarged or expanded geometry (FIG. 4) when placed outside the lumenof the sheath 300, and a collapsed geometry (FIG. 5) when disposedwithin the lumen 301 of the sheath 300. In the illustrated embodiment,liquid pressure is used to inflate and maintain theexpandable-collapsible body 330 in the expanded geometry. The electrodestructure 310(1) further includes an actuating internal electrode 350that supplies the body 330 with RF energy. Specifically, the internalelectrode 350 supplies RF energy through the medium that is used toinflate the body 330, which is then conveyed through pores 370 in thebody 330 to the surrounding tissue, as will be described in furtherdetail below.

The internal electrode 350 is carried at a distal end 352 of a supportmember 354, which is fixedly secured within the lumen 332 of thecatheter member 302 by cross bars 355 or similar structures. In analternative embodiment, the electrode 350 can be carried by a structure(not shown) fixedly secured to the distal end 306 of the catheter member302. In a further alternative embodiment, the electrode structure 310(1)does not include the cross bars 355, and the support member 354 isslidable within the lumen 332. This has the benefit of allowing thesupport member 354 to be removed from the interior 334 of the body 330,thereby allowing the body 330 to collapse into a lower profile. Theinterior electrode 350 is composed of a material that has both arelatively high electrical conductivity and a relatively high thermalconductivity. Materials possessing these characteristics include gold,platinum, platinum/iridium, among others. Noble metals are preferred. ARF wire 360 extends through the lumen 332 of the catheter member 302,and electrically couples the internal electrode 350 to the electricalconnector 362 on the handle assembly 320 (see FIG. 3). The supportmember 354 and/or the electrode structure 310 may carry temperaturesensor(s) (not shown) for sensing a temperature of a liquid inflationmedium 338 during use.

The distal end of the catheter lumen 332 is in fluid communication withthe hollow interior 334 of the expandable-collapsible body 330, and theproximal end of the lumen 332 is in fluid communication with the port336 on the handle assembly 320 (see FIG. 3). During use, the inflationmedium 338 is conveyed under positive pressure by the pump 409 throughthe port 336 and into the lumen 332. The liquid medium 338 fills theinterior 334 of the expandable-collapsible body 330, thereby exertinginterior pressure that urges the expandable-collapsible body 330 fromits collapsed geometry to its enlarged geometry.

The liquid medium 338 used to fill the interior 334 of the body 330establishes an electrically conductive path, which conveys radiofrequency energy from the electrode 350. In conjunction, the body 330comprises an electrically non-conductive thermoplastic or elastomericmaterial that contains the pores 370 on at least a portion of itssurface. The pores 370 of the body 330 (shown diagrammatically inenlarged form in FIGS. 4 and 5 for the purpose of illustration)establish ionic transport of ablation energy from the internal electrode350, through the electrically conductive medium 338, to tissue outsidethe body 330.

Preferably, the medium 338 possesses a low resistivity to decrease ohmicloses, and thus ohmic heating effects, within the body 330. In theillustrated embodiment, the medium 338 also serves the additionalfunction as the inflation medium for the body 330, at least in part. Thecomposition of the electrically conductive medium 338 can vary. In oneembodiment, the medium 338 comprises a hypertonic saline solution,having a sodium chloride concentration at or near saturation, which isabout 9%-15% weight by volume. Hypertonic saline solution has a lowresistivity of only about 5 ohm-cm, compared to blood resistivity ofabout 150 ohm-cm and myocardial tissue resistivity of about 500 ohm-cm.Alternatively, the composition of the electrically conductive liquidmedium 338 can comprise a hypertonic potassium chloride solution. Thismedium, while promoting the desired ionic transfer, requires closermonitoring of rate at which ionic transport occurs through the pores, toprevent potassium overload. When hypertonic potassium chloride solutionis used, it is preferred to keep the ionic transport rate below about 10mEq/min.

The size of the pores 370 can vary. Pore diameters smaller than about0.1 um, typically used for blood oxygenation, dialysis, orultrafiltration, can be used for ionic transfer. These small pores,which can be visualized by high-energy electron microscopes, retainmacromolecules, but allow ionic transfer through the pores in responseto an applied RF field. With smaller pore diameters, pressure drivenliquid perfusion through the pores 370 is less likely to accompany theionic transport, unless relatively high pressure conditions develop withthe body 330.

Larger pore diameters, typically used for blood microfiltration, canalso be used for ionic transfer. These larger pores, which can be seenby light microscopy, retain blood cells, but permit passage of ions inresponse to the applied RF field. Generally, pore sizes below 8 um willblock most blood cells from crossing the membrane. With larger porediameters, pressure driven liquid perfusion, and the attendant transportof macromolecules through the pores 370, is also more likely to occur atnormal inflation pressures for the body 330. Still larger pore sizes canbe used, capable of accommodating formed blood cell elements. However,considerations of overall porosity, perfusion rates, and lodgment ofblood cells within the pores of the body 330 must be taken more intoaccount as pore size increases.

Conventional porous, biocompatible membrane materials used for bloodoxygenation, dialysis, and blood filtration, such as plasmapheresis, canserve as the porous body 330. The porous body 330 can also be made from,for example, regenerated cellulose, nylon, polycarbonate,polytetrafluoroethylene (PTFE), polyethersulfone, modified acryliccopolymers, and cellulose acetate. Alternatively, porous or microporousmaterials may be fabricated by weaving a material (such as nylon,polyester, polyethylene, polypropylene, fluorocarbon, fine diameterstainless steel, or other fiber) into a mesh having the desired poresize and porosity. The use of woven materials is advantageous, becausewoven materials are very flexible.

Referring now to FIG. 6, another embodiment of a catheter 104(2) will bedescribed. Instead of using the lumen 332 of the catheter member 302 fordelivery of the liquid medium 338, as described in the previousembodiment, the ablation catheter 104(2) includes a separate deliverytube 339 positioned coaxially within the lumen 332 of the cathetermember 302 for delivering the liquid medium 338. In this case, theinternal electrode 350 is carried at a distal end of the tube 339. Theelectrode structure 310 also includes a sealer 341 secured to aninterior surface of the catheter member 302. In the illustratedembodiment, the tube 339 is secured to the sealer 341, which has a shapeand size configured to prevent delivered medium 338 from escaping fromthe interior 334 of the body 330.

The tube 339 is slidably secured to the sealer 341. This has the benefitof allowing the delivery tube 339 to be removed from the interior 334 ofthe body 330, thereby allowing the body 330 to collapse into a lowerprofile. In this case, the sealer 341 has a shape and size configured toprevent delivered medium 338 from escaping from the interior 334 of thebody 330, while allowing the tube 339 to slide therethrough.Alternatively, if a sliding arrangement between the tube 339 and thebody 330 is not required or desired, the delivery tube 339 can besecured to the proximal end of the body 330.

The proximal end of the delivery tube 339 is coupled to the pump 409during use. The body 330 can be inflated by the medium 338 delivered viathe delivery tube 339, and deflated by discharging the medium 338 alsothrough the delivery tube 339. In an alternative embodiment, thecatheter 104(2) does not include the sealer 341, and the lumen 332 ofthe catheter member 302 outside the delivery tube 339 can be used toreturn medium to the proximal end of the ablation catheter 104(1).Alternatively, the delivery tube 339 may have an outer diameter that issubstantially the same as the opening at the proximal end of the body330, thereby forming a substantially water-tight interface between thedelivery tube 339 and the body 330 (FIG. 7). In this case, the tube 339includes a separate discharge lumen 343 disposed within the wall of thetube 339 for carrying medium 338 away from the body 330.

As FIGS. 8-10 show, the electrode structure 310 can include, if desired,a normally open, yet collapsible, interior support structure 340 toapply internal force to augment or replace the force of liquid mediumpressure to maintain the body 330 in the expanded geometry. The form ofthe interior support structure 340 can vary. It can, for example,comprise an assemblage of flexible spline elements 342, as shown in theelectrode structure 310(2) of FIG. 8 (expanded geometry) and FIG. 9(collapsed geometry), or an interior porous, interwoven mesh or an openporous foam structure 344, as shown in the electrode structure 310(3) ofFIG. 10. The interior support structure 340 is located within theinterior 334 of the body 330 and exerts an expansion force to the body330 during use. Alternatively, the interior support structure 340 can beembedded within the wall of the body 330. The interior support structure340 can be made from a resilient, inert material, like nickel titanium(commercially available as Nitinol material), or from a resilientinjection molded inert plastic or stainless steel. The interior supportstructure 340 is preformed in a desired contour and assembled to form athree dimensional support skeleton.

Referring now to FIGS. 11-13, further embodiments of an electrodestructure 310 are described. The stabilizer 400 is not shown for thepurpose of clarity. Rather than having a porous body 330 and an interiorelectrode 350, as with the previous embodiments, the electrodestructures 310 illustrated in FIGS. 11A-11C comprise a non-porousexpandable-collapsible body 330, and an electrically conductive layerassociated with the non-porous body 330.

For example, FIG. 11A illustrates one embodiment of an electrodestructure 310(4) that includes an electrically conducting shell 380disposed upon the exterior of the formed body 330. The electrodestructure 310 also includes a RF wire 381 (FIGS. 12 and 13) thatelectrically connects the shell 380 to the ablation source 108. The RFwire 381 may be embedded within the wall (FIG. 12) of the body 330, oralternatively, be carried within the interior 334 of the body 330 (FIG.13). Ablation energy is delivered from the ablation source 108, via theRF wire 381, to the shell 380.

In the illustrated embodiment, the shell 380 is deposited upon thesurface of the body 330. Preferably, the shell 380 is not deposited onthe proximal one-third surface of the body 330. This requires that theproximal surface of the body 330 be masked, so that no electricallyconductive material is deposited there. This masking is desirablebecause the proximal region of the electrode structure 310 is notnormally in contact with tissue. The shell 380 may be made from avariety of materials having high electrical conductivity, such as gold,platinum, and platinum/iridium. These materials are preferably depositedupon the unmasked, distal region of the body 330. Deposition processesthat may be used include sputtering, vapor deposition, ion beamdeposition, electroplating over a deposited seed layer, or a combinationof these processes. To enhance adherence between theexpandable-collapsible body 330 and the shell 380, an undercoating 382is first deposited on the unmasked distal region before depositing theshell 380. Materials well suited for the undercoating 382 includetitanium, iridium, and nickel, or combinations or alloys thereof.

FIG. 11B illustrates another embodiment of an electrode structure 310(5)in which the shell 380 comprises a thin sheet or foil 384 ofelectrically conductive metal affixed to the wall of the body 330.Materials suitable for the foil include platinum, platinum/iridium,stainless steel, gold, or combinations or alloys of these materials. Thefoil 384 preferably has a thickness of less than about 0.005 cm. Thefoil 384 is affixed to the body 330 using an electrically insulatingepoxy, adhesive, or the like.

FIG. 11C illustrates still another embodiment of an electrode structure310(6) in which all or a portion of the expandable-collapsible wallforming the body 330 is extruded with an electrically conductivematerial 386. Materials 386 suitable for coextrusion with theexpandable-collapsible body 330 include carbon black and chopped carbonfiber. In this arrangement, the coextruded expandable collapsible body330 is itself electrically conductive. An additional shell 380 ofelectrically conductive material can be electrically coupled to thecoextruded body 330, to obtain the desired electrical and thermalconductive characteristics. The extra external shell 380 can beeliminated, if the coextruded body 330 itself possesses the desiredelectrical and thermal conductive characteristics. The amount ofelectrically conductive material coextruded into a given body 330affects the electrical conductivity, and thus the electrical resistivityof the body 330, which varies inversely with conductivity. Addition ofmore electrically conductive material increases electrical conductivityof the body 330, thereby reducing electrical resistivity of the body330, and vice versa.

The above described porous and non-porous expandable-collapsible bodiesand other expandable structures that may be used to form the electrodestructure 310 are described in U.S. Pat. Nos. 5,846,239, 6,454,766 B1,and 5,925,038, the entire disclosures of which are expresslyincorporated by reference herein.

Refer to FIGS. 14-18, the stabilizer 400 and the portion of the ablationcatheter 104 in association with the stabilizer 400 will now bedescribed. As shown in FIGS. 14 and 15, one embodiment of a stabilizer400(1) includes a shroud 402 that is secured to the distal end 306 ofthe catheter member 302. The shroud 402 circumscribes at least a portionof the expandable-collapsible body 330, thereby substantially preventingablation energy from dissipating to surrounding tissues beyond thetarget tissue to be ablated. The stabilizer 400(1) further comprises aplurality of vacuum ports 407 (here, four) associated with a distal edge405 of the shroud 402, and a plurality of respective vacuum lumens 404longitudinally extending within a wall of the shroud 402 in fluidcommunication with the vacuum ports 407. The stabilizer 400(1) includesan optional temperature sensing element 414, such as a thermocouple orthermistor, secured to the shroud 402. The temperature sensing elements414 may be used to monitor a tissue temperature.

To provide vacuum force to the stabilizer 400(1), the ablation catheter104 comprises a main vacuum lumen 406 embedded with the wall of thecatheter member 302. The lumen 406 is in fluid communication between thevacuum lumens 404 on the shroud 402 and the vacuum port 408 located onthe handle assembly 320. During use of the ablation catheter 104, thevacuum port 408 is coupled to the vacuum 598, which generates a vacuumor a vacuum force within the vacuum lumens 404 of the stabilizer 400(1).

The shroud 402 is made from a material having low electricalconductivity, such as a polymer, plastic, silicone, or polyurethane. Theshroud 402 has enlarged planar regions 410 for carrying the vacuumlumens 404, and thinner planar regions 412 for allowing the shroud 402to fold into a low profile during use (FIG. 15). Alternatively, if thevacuum lumens 404 are sufficiently small, the shroud 402 can have asubstantially uniform wall thickness. Although four enlarged planarregions 410 are shown, the shroud 402 can have fewer or more than fourplanar regions 410, depending on the number of vacuum lumens 404.

In the illustrated embodiment, the stabilizer 400(1) is secured to theexterior surface of the expandable-collapsible body 330. In thisconfiguration, the stabilizer 400 will be pushed open by the body 330 toits expanded configuration when the body 330 is inflated, and pulled toits collapsed configuration when the body 330 is deflated.Alternatively, the stabilizer 400(1) is not secured to the body 330, inwhich case, the stabilizer 400(1) will be pushed open by a bearing forceexerted by the body 330 when the body 330 is expanded, and will assume acollapsed configuration when the electrode structure 310 is confinedwithin a lumen of the sheath 300.

As shown in FIG. 16, the stabilizer 400(1) optionally includes supportwires 430, which are partially embedded within the wall of the shroud402 and partially within the wall of the catheter member 302. Thesupport wires 430 can be made from a resilient material, such as metalor plastic. Nitinol is particularly preferred. In one embodiment, thesupport wires 430 are preformed to have a shape that is substantiallyrectilinear. In this case, the shroud 402 will remain substantially inits collapsed configuration until pushed to open into an expandedconfiguration by the expandable-collapsible body 330 when the body 330is expanded. Such configuration has the benefit of allowing theelectrode structure 310 to assume its collapsed configuration moreeasily. If the support wires 430 are made stiff enough, the electrodestructure 310 together with the stabilizer 400(1) can assume theircollapsed configurations without the use of the sheath 300. In thiscase, the sheath 300 is optional and the ablation catheter 104 does notinclude the sheath 300. In an alternative embodiment, the support wires430 are preformed to have a bent shape that flares away from acenterline 432 at the distal end 306 of the catheter member 302. In thiscase, the stabilizer 400(1) will assume a collapsed configuration whenresided within a lumen of a sheath 300, and will have a tendency to openinto the expanded configuration when it extends distally from the sheath300. Such configuration has the benefit of allowing the electrodestructure 310 to assume its expanded configuration more easily.

FIG. 17 shows another embodiment of a stabilizer 400(2) that does notcontinuously circumscribe a portion of the body 330 as did thepreviously described stabilizer 400(1). Instead, the stabilizer 400(2)comprises a plurality of tubes 420 (in this case, two) that extend alongthe length of the body 330. The tubes 430 may or may not be secured tothe body 330. Each of the tubes 430 has a vacuum lumen 422 and anassociated vacuum port 423 at its distal end. The proximal end of eachtube 420 is in fluid communication with the vacuum port 408 located onthe handle assembly 320 (shown in FIG. 3). The tubes 420 includeoptional support wires 430 to provide a pre-shaped geometry, aspreviously described with respect to the shroud 402 of the stabilizer400(1).

In all of the above-described embodiments, the stabilizer 400 isexterior to the expandable-collapsible body 330. FIG. 18 shows anotherembodiment of a stabilizer 400(3) that is internal to the body 330. Asshown in the illustrated embodiment, the stabilizer 400(3) includes avacuum tube 450 located within the interior 334 of theexpandable-collapsible body 330. The vacuum tube 450 includes a distalend 452 that is secured to the distal portion of the body 330. The tube450 has a vacuum lumen 454 and an associated vacuum port 456 at itsdistal end. The proximal end of the tube 420 is in fluid communicationwith the vacuum port 408 at the handle assembly 320 (shown in FIG. 3).The vacuum tube 450 carries the electrode 350, thus obviating the needfor the previously described support member 354.

Although the ablation catheter 104 has been described as havingelectrode structures 310 with expandable-collapsible bodies, it shouldbe noted that the ablation catheter 104 can have other electrodestructure configurations. For example, FIG. 19A illustrates anotherembodiment of an ablation catheter 104(3), which includes a cathetermember 462, an electrode structure 310(7) and stabilizer 400(4) mountedto the distal end 464 of the catheter member 462, and a handle assembly461 mounted to the proximal end 465 of the catheter member 462. Thehandle assembly 461 is similar to the previously described handleassembly 320, with the exception that it does not include a fluid port,since there is no expandable/collapsible body.

The electrode structure 310(7) does not include anexpandable-collapsible body, but rather a rigid cap-shaped electrode 460mounted to the distal tip of the catheter member 462. The electrodestructure 310(7) further comprises a RF wire 468 that is electricallycoupled between the electrode 460 and the electrical connector 362 onthe handle assembly 461. The RF wire 468 extends through a lumen 466 ofthe catheter member 462. The stabilizer 400(4) includes one or morevacuum lumens 470 (in this case, two) embedded within the wall of thecatheter member 462. The distal ends of the vacuum lumens 470 terminatein vacuum ports 472, and the proximal ends of the vacuum lumens 470 arein fluid communication with the vacuum port 408 on the handle assembly461.

In an alternative embodiment, the lumen 466 may also be used to delivercooling medium to the electrode 460 for active cooling the electrode 460during use. In the illustrated embodiment, the electrode 460 does nothave any outlet port, and therefore, the ablation catheter 104(3) can beused to perform closed loop cooling in which cooling medium is deliveredto the electrode 460 and circulate back to a proximal end of theablation catheter 104(3). Alternatively, the electrode 460 can have oneor more outlet ports for performing open loop cooling in which coolingmedium is delivered to the electrode 460 and is at least partiallydischarged through the outlet port for cooling the outside of theelectrode 460. Ablation catheters capable of performing closed loopcooling and open loop cooling are described in U.S. Pat. No. 5,800,432,the entire disclosure of which is expressly incorporated by referenceherein.

FIG. 19B shows another embodiment of the ablation catheter 104(4), whichis similar to the previously described ablation catheter 104(3), withthe exception that it includes a sheath 484 and a catheter member 480that is slidably disposed within the lumen 486 of the sheath 484. Ratherthan being disposed within the catheter member 480, the vacuum lumens488 are disposed along the length of the sheath 484. In this case, thedistal end 489 of the sheath 484 acts as the stabilizer. The sheath 484also includes a vacuum port 490 that is in fluid communication with thevacuum lumens 488. It should be noted that the ablation device that canbe used with the system 100 should not be limited to the embodiments ofthe ablation catheters 104(1)-104(4) discussed previously, and thatother ablation devices known in the art may also be used. For examples,ablation catheters such as modified versions of those described in U.S.Pat. Nos. 5,800,432, 5,925,038, 5,846,239 and 6,454,766 B1, can be usedwith the system 100.

The Ground Probe

The ground catheter 106 will now be described with reference to FIGS.20-26. In the embodiment shown in FIGS. 20 and 21, a ground catheter106(1) includes a catheter member 600 having a proximal end 602 and adistal end 604, a plurality of electrode elements 606 carried on thedistal end 604, and a handle assembly 608 secured to the proximal end602. The catheter member 600 is made of, for example, a polymeric,electrically nonconductive material, such as polyethylene orpolyurethane or PEBAX™ material (polyurethane and nylon). The handleassembly 608 includes a handle 609 for providing a means for thephysician to manipulate the catheter member 600, and an electricalconnector 610 coupled to the ablation source 108 for providing ablationenergy to the electrode elements 606. The handle assembly 608 alsoincludes a steering mechanism 612 for steering the distal end 604. Thesteering mechanism 612 is similar to the steering mechanism 500discussed previously with reference to the ablation catheter 104.Furthermore, the ground catheter 106(1) may carry temperature sensor(s)(not shown) for monitoring a temperature of a tissue.

The electrode elements 606 function as indifferent electrodes and areconfigured to complete an electrical path from within a body of apatient. Each electrode element 606 has a suitable dimension along thelength of the catheter member 600, e.g., 2 inches. The electrodeelements 606 can be assembled in various ways. In the illustratedembodiment, the electrode elements 606 are arranged in a spaced apart,segmented relationship along the catheter member 600. Specifically, theelectrode elements 606 comprise spaced apart lengths of closely wound,spiral coils wrapped about the catheter member 600 to form an array ofgenerally flexible electrode elements 606. The coils are made ofelectrically conducting material, like copper alloy, platinum, orstainless steel, or compositions such as drawn-filled tubing. Theelectrically conducting material of the coils can be further coated withplatinum-iridium or gold to improve its conductive properties andbiocompatibility.

Alternatively, the segmented electrode elements 606 can each comprisesolid rings of conductive material, like platinum, which makes aninterference fit about the catheter member 600. Even more alternatively,the electrode segments 606 can comprise a conductive material, likeplatinum-iridium or gold, coated upon the catheter member 600 usingconventional coating techniques or an ion beam assisted deposition(IBAD) process.

Because the electrode elements 606 function as indifferent electrodesfor returning energy to the ablation source 108, it would be desirableto maximize the space occupied by the electrode elements 606 and thenumber of electrode elements 606 within such space. Towards this end,the distal end 604 of the catheter member 600 and/or the electrodeelements 606 is made sufficiently flexible such that the distal end 604of the catheter member 600 can assume a configuration to at leastpartially fill a body cavity 620, as shown in FIG. 21.

To prevent the heated electrode elements 606 of the ground catheter106(1) from damaging healthy tissue, the ground catheter 106(1) furtherincludes a cage assembly 660 disposed around each electrode 606 toprevent it from making contact with tissue, and a sheath 630 fordeploying the cage assembly 660. As shown in FIG. 22, the cage assembly660 includes a proximal end 662, a distal end 664, and a plurality ofstruts 666 secured between the proximal end 662 and the distal end 664.At least one of the proximal end 662 and the distal end 664 is a ringelement (FIG. 22). In the illustrated embodiment, the cage assembly 660has eight struts. In alternative embodiments, the cage assembly 660 mayhave more or less than eight struts 666. The struts 666 are made from anon-electrically conductive and elastic material, such as a polymer.Alternatively, if insulation is provided between the cage assembly 660and the electrode elements 606, the struts 666 can also be made frommetal, such as stainless steel or Nitinol.

The cage assembly 660 assumes an expanded configuration when it isoutside the sheath 630 (FIG. 22). The cage assembly 660, in its expandedconfiguration, prevents the electrode elements 606 from making contactwith adjacent tissue during use. The spacing between the struts 666allow medium, such as blood or other bodily fluid, to flow through andmake contact with the electrode elements 606. Since blood and otherbodily fluid contains ions, allowing blood or other bodily fluid to makecontact with the electrode elements 606 assists completion of thecurrent path between the electrode structure 310 and the electrodeelements 606. The proximal end 662 and the distal end 664 are fixedlyand slidably secured, respectively, to the catheter member 600. When thecatheter member 600 is retracted proximally relative to the sheath 630,the sheath 630 compresses the struts 666 and causes the distal end 664of the cage assembly 660 to slide distally relative to the cathetermember 600 (FIG. 23). In an alternative embodiment, the distal end 664of the cage assembly 660 is fixedly secured to the catheter member 600and the proximal end 662 is slidable relative to the catheter member600.

Although in the previously described embodiment, the cage assembly 660is shown to at least partially cover a single electrode element 606, inalternative embodiments, the cage assembly 660 partially covers morethan one electrode element 606. Furthermore, it should be noted that thecage assembly 660 is not limited to the configurations shown previously.For example, in alternative embodiments, the cage assembly 660 cancomprise a braided or woven material secured to the struts 666. Inanother embodiment, the cage assembly 660 can comprise a braided orwoven material that is elastic, in which case, the cage assembly 660does not include the struts 666. Also, in another embodiment, instead ofa cage assembly, the ground catheter can include other types ofprotective element, such as a wire or a plate, that at least partiallycovers an electrode.

FIGS. 24-26 show another embodiment of a ground catheter 106(2) that maybe used with the system 100 of FIG. 1. As shown in FIG. 24, the groundcatheter 106(2) includes a sheath 630 having a lumen 632, and a cathetermember 634 slidable within the lumen 632 of the sheath 630. The catheter106(2) comprises a plurality of electrodes 636 mounted on the distal endof the catheter member 634. The catheter member 634 and electrodeelements 636 are similar to the previously described catheter member 600and the electrode elements 606. Although not shown, the catheter 106(2)may also include one or more cage assemblies at least partially coveringone or more of the electrodes 636, as discussed previously.

The catheter 106(2) further comprises a resilient spring member 642 thatis suitably connected between the distal end 640 of the sheath 630 andthe distal tip 638 of the catheter member 634. In the illustratedembodiment, the spring member 642 comprises a wire made of an elasticmaterial, such as Nitinol, and is secured to an interior surface of thesheath 630. Alternatively, the spring member 642 can also be secured toan exterior surface of the sheath 630 (FIG. 26). Also, in alternativeembodiments, the spring member 642 may be a coil or an extension of thecatheter member 634, and may be made of other elastic materials, such asmetals or plastics.

As shown in FIG. 25, distal movement of the proximal end 644 of thecatheter member 634 relative to the sheath 630 deploys the cathetermember 634 out of the distal end 640 of the sheath 630, and forms thecatheter member 634 into a loop shape to thereby deploy the electrodes636. In an alternative embodiment, a wire (not shown) preformed into adesired shape may be placed within the catheter member 634, such thatwhen the catheter member 634 is deployed out of the distal end 640, thecatheter member 634 will bend into a desired configuration.

The above-described devices and other similar devices having loopforming capability that may be used with the system 100 are described inU.S. Pat. No. 6,330,473, as mentioned herein. Furthermore, inalternative embodiments, the ground catheter 106 does not include a cageassembly. For example, internal indifferent electrode device, such asthat described in U.S. patent application Ser. No. 09/801,416, can alsobe used as the ground catheter 106. U.S. patent application Ser. No.09/801,416 is hereby expressly incorporated by reference in itsentirety.

Mapping Catheter

Turning now to FIGS. 27-29, the details of the mapping catheter 700 willbe described. The mapping catheter 700 is configured for sensingelectrical signals at a heart to thereby determine a target location atthe heart to be ablated.

FIG. 27A shows an embodiment of a mapping catheter 700(1) that may beused with the system 100 for sensing signals on a surface of a heart.The mapping catheter 700 includes an actuating sheath 712 having a lumen713, and a catheter member 708 slidably disposed within the lumen 713 ofthe sheath 712. The catheter member 708 comprises a proximal end 709 anda distal end 710, and an electrode array structure 702 mounted to thedistal end 710 of the catheter member 708. The electrode array structure702 includes a plurality of resilient spline elements 704, with eachspline element 704 carrying a plurality of mapping electrodes 706. Eachof the spline elements 704 further includes a vacuum port 716 coupled tothe vacuum 732 (shown in FIG. 1) via a lumen (not shown) carried withinthe spline element 704. The vacuum ports 716 are configured to apply avacuum force to stabilize the array structure 702 relative to tissue asthe mapping electrodes 706 sense electrical signals at the tissue. Thenumber of spline elements 704 and electrodes 706 may vary, but in theillustrated embodiment, there are eight spline elements 704, with fourmapping elements 706 on each spline element 704. The array 702 isconfigured to assume an expanded configuration, as shown in FIG. 27A,when it is outside the sheath 712. The size and geometry of the array702 are configured such that the array 702 can at least partially coverthe epicardial surface of a heart when it is in its expandedconfiguration. Because the mapping catheter 700(1) is not configured tobe steered through vessels, as in the case with conventional mappingcatheters, the array 702 can be made relatively larger to carry moremapping electrodes 706. The array 702 is also configured to be broughtinto a collapsed configuration by retracting the array 702 (i.e.,proximally moving a handle 714 secured to the probe 708) into the lumenof the sheath 712 (FIG. 27B).

The mapping catheter 700(1) further includes a handle assembly 714mounted to the proximal end 709 of the catheter member 708. The handleassembly 714 includes an electrical connector 715 coupled to theprocessor 730 for processing signals sensed by the mapping electrodes706 to thereby determine a target site to be ablated. The handleassembly 714 also includes a port 717 coupled to the vacuum 732 forgenerating a vacuum force at the vacuum ports 716.

FIG. 28A shows another embodiment of the mapping catheter 700(2), whichis similar to the previously described embodiment. However, instead ofan array 702 of spline elements 704, the mapping catheter 700(2)includes a grid or a mesh like structure 720 carrying a plurality ofmapping electrodes 706. The grid 720 is preferably made from anelectrically non-conductive material, such as a polymer. However, othermaterials may also be used for construction of the grid 720. The grid720 assumes an expanded configuration (FIG. 28A) when it is outside thesheath 712, and assumes a collapsed configuration by proximally movingthe handle 714 relative to the sheath 712, thereby retracting the grid720 into the lumen of the sheath 712 (FIG. 28B). Although not shown, themapping catheter 700(2), like the previously described mapping catheter700(1), may also include stabilizing functionality.

FIG. 29A shows another embodiment of a mapping catheter 700(3), whichincludes a linear structure 722 carrying a plurality of mappingelectrodes 706. The structure 722 is preferably made from anelectrically non-conductive material, such as a polymer. However, othermaterials may also be used for construction of the structure 722. Thestructure 722 assumes the spiral expanded configuration when it isoutside the sheath 712 (FIG. 29A), and assumes a collapsed configurationby proximally moving the handle 714 relative to the sheath 712, therebyretracting the structure 722 into the lumen of the sheath 712 (FIG.29B). Although not shown, the mapping catheter 700(3), like thepreviously described mapping catheter 700(1), may also includestabilizing functionality.

Method of Use

Refer to FIGS. 30A-30D, a method of using the system 100 will now bedescribed with reference to cardiac ablation therapy. Particularly, themethod will be described with reference to the embodiment of the cannula201 shown in FIG. 2, the embodiment of the ablation catheter 104(1)shown in FIG. 3, the embodiment of the ground catheter 106(2) shown inFIG. 24, and the embodiment of the mapping catheter 700(1) shown in FIG.27. However, it should be understood by those skilled in the art thatsimilar methods described herein may also apply to other embodiments ofthe system 100 previously described, or even embodiments not describedherein.

When using the system 100 for cardiac ablation therapy, a physicianinitially makes an incision through a patient's skin 800 to form anopening 801. For example, a small incision or port in the intercostalsspace or subxiphoid may be created by a trocar (not shown). Next, thecannula 201 is inserted through the opening 801 (FIG. 30A) to reach thepericardial space of the chest cavity. The cannula 201 is distallyadvanced into the patient's body until the stopper 224 bear against thepatient's skin 800 or against a trocar (not shown). If the position ofthe stopper 224 is adjustable, such as that shown in FIG. 2A, theposition of the stopper 224 may be adjusted before and/or after thecannula 201 is inserted into the opening 801. The imaging device 214 andthe light source 220 may be used to monitor the distance between thedistal tip of the cannula 201 and the heart 802 as the cannula 201 isdistally advanced into the body. Other procedures, such as a MinimallyInvasive Direct Coronary Artery Bypass (MIDCAB) procedure, aconventional thoracotomy, ministernotomy, or thorascopic technique, mayalso be used to access the heart 802.

Next, the physician determines a location of a target tissue on theheart 802 to be ablated. Particularly, the mapping catheter 700(1) isemployed to sense electrical signals at the heart 802, and determine atarget tissue to be ablated, e.g., the region responsible for VT. Tothis end, the mapping catheter 700(1) is inserted into the lumen 208 ofthe cannula 201 and distally advanced until it exits from the distal end206 of the cannula 201. As shown in FIG. 30B, the mapping catheter700(1) is deployed, such that the mapping electrodes 706 are in contactwith the epicardial surface 806 of the heart 802. The vacuum 732 isactivated to create a vacuum within the ports 716, thereby forcing theepicardial surface 806 towards the spline elements 704 of the mappingcatheter 700(1) and maintaining the cardiac tissue substantially inplace relative to the array structure 702. Thus, relative movementbetween the mapping electrodes 706 and the epicardial surface 806 of theheart 802 is prevented, or at least minimized.

In the illustrated method, the mapping catheter 700(1) is configured tosense electrical signals at an exterior surface of the heart 802.Performing signal sensing on the exterior of the heart 802 is beneficialin that the physician can readily move the mapping catheter 700(1)around the heart 802 to obtain data at different locations on the heart802. Once a target site is determined, it can then be marked with abiocompatible surgical ink, which can be visualized by a conventionalimaging device. For example, surgical ink can be delivered through anorifice of a catheter to mark the target site. Performing signal sensingon the exterior of the heart 802 also reduces the risk of blocking ablood vessel and/or puncturing a vessel associated with mappingprocedures that require a catheter steered through vessels.Alternatively, instead of performing signal sensing on the exterior ofthe heart 802, a suitable mapping catheter may be inserted through avein or artery, steered to an interior of the heart 802, and be used tomap electrical signals from within the heart 802 using a conventionalmethod. In an alternative embodiment, the determination of the locationof the target tissue is determined using a conventional method in aseparate procedure before the operation.

For the purpose of the following discussion, it will be assumed that thetarget area to be ablated has been determined in the mapping session tobe at the right ventricle of the heart 802. However, it should beunderstood that the method described herein is also applicable forperforming ablation at other areas of the heart 802.

Prior to ablation, the distal end of the ground catheter 106(2) isinserted through a main vein or artery (typically the femoral vein orartery), and is steered into an interior region 804, particularly, theright ventricular chamber, of the heart (FIG. 30C). The ground catheter106(2) can be steered by manipulating the handle assembly 608 and/oroperating the steering mechanism 612 on the handle 608. Because theright ventricular chamber has a relatively wide space, the distal end ofthe ground catheter 106 can be bent or folded into a more voluminousconfiguration as described previously with reference to FIG. 25.

Next, the mapping catheter 700(1) is removed from the lumen 208 of thecannula 201. The distal end of the ablation catheter 104(1) is theninserted into the lumen 208 of the cannula 201, and distally advanceduntil it is adjacent the epicardial surface 806 of the heart 802 (FIG.30D). Alternatively, if the cannula 201 has a dual lumen, such as thatshown in FIG. 2C, the catheter 104(1) may be inserted into a secondlumen of the cannula 201 while the mapping catheter 700(1) remains inthe other lumen of the cannula 201, thereby avoiding the need to removethe mapping catheter 700(1). As shown in FIG. 30D, the electrodeelements 636 of the ground catheter 106(2) are preferably placed in abody cavity that is next to and on one side 810 of the target tissuewhile the ablation catheter 104(1) is placed on the opposite side 812 ofthe target tissue. Particularly, the ablation catheter 104(1) ispositioned adjacent a surface of the heart while the ground catheter 106is positioned within the right ventricular chamber, such that a line 850connecting the electrode structure 310 and the electrode elements 636penetrates a thickness of the target tissue. The physician can furthermanipulate the ablation catheter 104(1) to place the electrode structure310 in close proximity to the epicardial surface 806 of the heart thatis targeted for ablation. For example, the physician may operate thesteering lever 502 on the handle assembly 320 to steer the electrodestructure 310, or move (i.e., torque or axially position) the handleassembly 320, for positioning the electrode structure 310. In theillustrated embodiment, the electrode structure 310 is positioned at theanterior of the heart 802 for ablation of a target area in the rightventricle. Alternatively, for ablation of other areas in the heart, theelectrode structure 310 may be steered to other regions of the heart802, such as the posterior of the heart 802.

The electrode structure 310 of the ablation catheter 104(1) is confinedwithin the lumen of the sheath 300 as the ablation catheter 104(1) isdistally advanced into the cardiac space. After the distal end of theablation catheter 104(1) exits from the distal end 206 of the cannula201, the sheath 300 is proximally retracted relative to the cathetermember 302 until the electrode structure 310 exits from the distal endof the sheath 300. Alternatively, if the ablation catheter 104(1) doesnot include the sheath 300, the physician may use the lumen 208 of thecannula 201 to confine the electrode structure 310 as it is advancedthrough the cannula 201.

Medium 338 is then delivered from the pump 409 that is coupled to theinlet port 336 on the handle assembly 320, to the interior 334 of theexpandable-collapsible body 330 to inflate the body 330. Inflation ofthe body 330 will cause the stabilizer 400(1) to change from itscollapsed configuration to an expanded configuration.

After the body 330 is inflated, the electrode structure 310 is furtherdistally advanced such that the distal portion of the body 330 and thestabilizer 400(1) is in contact with the epicardial surface 806 of theheart 802 at the target tissue. The vacuum 598 is activated to create avacuum within the ports 407 of the stabilizer 400(1), thereby forcingbody 330 of the ablation catheter 104(1) towards the epicardial surface806 and maintaining the cardiac tissue substantially in place relativeto the body 330. Thus, relative movement between the electrode structure310(1) and the epicardial surface 806 of the heart 802 is prevented, orat least minimized.

Next, with the ablation catheter 104(1) coupled to the output port ofthe RF generator 108, and the ground catheter 106(2) coupled to thereturn/ground port of the RF generator 108, ablation energy is deliveredfrom the generator 108 to the electrode structure 310 of the ablationcatheter 104(1). If the electrode structure 310 includes the expandableporous body 330 with the internal electrode 350 (see FIGS. 4-10), RFenergy is delivered from the generator 108 to the electrode 350 via theRF wire 360. Electric current is transmitted from the electrode 350 tothe ions within the medium 338 within the body 330. The ions within themedium 338 convey RF energy through the pores 370 into the targettissue, and to the electrode elements 636 on the ground catheter 106. Ifthe electrode structure 310 includes the expandable body 330 with theconducting shell 380 (see FIGS. 11A-11C), RF energy is delivered fromthe generator to the conducting shell 380 via the RF wire 381. In thiscase, the conducting shell 380 directly transmits the RF energy to thetarget tissue.

By placing the ground catheter 106(2) within the heart 802, the path ofthe current delivered by the electrode structure 310 is shorter, i.e.,RF energy is directed from the electrode structure 310, across thetarget tissue, and to the electrode elements 636 of the ground catheter106(2), thereby efficiently forming a transmural lesion 808 at thetarget tissue. Such configuration also allows the target tissue to beablated without a significant dissipation of RF energy to adjacenttissues.

During the ablation process, the electrode 350 or the body 330delivering ablation energy may overheat, thereby causing tissue charringand preventing formation of a deeper lesion. This may negatively affectthe ablation catheter's ability to create a desirable lesion. In theillustrated embodiment, the inflation medium 338 used to inflate thebody 330 may be used to cool the internal electrode 350. Alternatively,an ablation catheter having active cooling capability, such as thecatheter 104(3) described previously with reference to FIG. 19A, may beused. The use of active cooling in association with the transmission ofDC or radio frequency ablation energy is known to force theelectrode-tissue interface to lower temperature values. As a result, thehottest tissue temperature region is shifted deeper into the tissue,which in turn, shifts the boundary of the tissue rendered nonviable byablation deeper into the tissue. An electrode that is actively cooledcan be used to transmit more ablation energy into the tissue, comparedto the same electrode that is not actively cooled.

During the ablation process, the electrode elements 636 may also heatup. However, the cage assemblies 660 of the ground catheter 106(2)prevents the electrode elements 636 from directly touching the healthytissue, thereby preventing ablation of adjacent healthy tissue.

After a desired lesion 808 at the right ventricle on the heart 802 hasbeen created, the medium 338 within the body 330 is discharged todeflate the body 330. The ablation catheter 104(1) and the groundcatheter 106(2) are then retracted and removed from the interior of thepatient.

In the previously described method, the system 100 is used to ablate atarget tissue in a quasi-bipolar arrangement, i.e., an ablationstructure and a return electrode are placed inside a body with aconfiguration such that a line connecting the ablation structure and thereturn electrode penetrates a thickness of the target tissue. The system100 may also be used to ablate a target tissue in other quasi-bipolararrangements.

For example, rather than placing the ground catheter 106 in the rightventricular chamber, the ground catheter 106 can be placed in otherregions of the heart. For example, the ground catheter 106 may be placedwithin a vein, such as a pulmonary vein, an artery, a coronary sinus, aleft ventricle, an inferior vena cava, or other cavity within the heart802. If the ground catheter 106 is placed in a narrow lumen, as in avein, the distal end of the ground catheter 106 can be placed within theregion 804 such that the profile of the ground catheter 106approximately conforms with the contour of the lumen. For example, thedistal portion of the ground catheter 106 can have a curvilinearconfiguration that circumscribes the pulmonary vein in the left atriumof the heart 802. Furthermore, the ground catheter 106 can be placedwithin a body but external to the heart, while the ablation catheter 104is placed within the heart.

In another quasi-bipolar arrangement, both the ablation catheter 104 andthe ground catheter 106 are positioned within the heart, with theablation catheter 104 placed at the target tissue within the heart, andthe ground catheter 106 placed at another position adjacent the targettissue, such that a line connecting between the electrode structurecarried on the ablation catheter 104 and an electrode element carried onthe ground catheter 106 penetrates through a thickness of the targettissue. For example, the system 100 described previously can be used tocreate lesions inside the left atrium between the pulmonary veins andthe mitral valve annulus. Tissue nearby these anatomic structures arerecognized to develop arrhythmia substrates causing atrial fibrillation.Lesions in these tissue regions block reentry paths or destroy activepacemaker sites, and thereby prevent the arrhythmia from occurring.

For example, FIG. 31 shows (from outside the heart H) the location ofmajor anatomic landmarks for lesion formation in the left atrium. Thelandmarks include the right inferior pulmonary vein (RIPV), the rightsuperior pulmonary vein (RSPV), the left superior pulmonary vein (LSPV),the left inferior pulmonary vein (LIPV); and the mitral valve annulus(MVA). FIGS. 32A and 32B show examples of lesion patterns formed insidethe left atrium based upon these landmarks.

In FIG. 32A, the lesion pattern comprises a first leg L1 between theright inferior pulmonary vein (RIPV) and the right superior pulmonaryvein (RSPV); a second leg L2 between the RSPV and the left superiorpulmonary vein (LSPV); a third leg L3 between the left superiorpulmonary vein (LSPV) and the left inferior pulmonary vein (LIPV); and afourth leg L4 leading between the LIPV and the mitral valve annulus(MVA). The first, second, and third legs L1-L3 can be created in aquasi-bipolar manner by directing ablation energy to the ablationcatheter 104 that is placed at the left atrium (LA), while the groundcatheter 106 is placed inside the left ventrical (LV), the rightventrical (RV), or the coronary sinus (CS). The fourth leg L4 can becreated by directing ablation energy to the ablation catheter 104 thatis placed at the LA, while the ground catheter 106 is placed inside theCS. In alternative methods, the positions of the ablation catheter 104and the ground catheter 106 described previously may be exchanged.

FIG. 32B shows a criss-crossing lesion pattern comprising a first leg L1extending between the RSPV and LIPV; a second leg L2 extending betweenthe LSPV and RIPV; and a third leg L3 extending from the LIPV to theMVA. The first and second legs L1, L2 can be created by directingablation energy to the ablation catheter 104 placed at the LA, while theground catheter 106 is placed inside the LV, RV, or the CS. The thirdleg L3 can be created by directing ablation energy to the ablationcatheter 104 placed at the LA, while the ground catheter 106 is placedinside the CS. In alternative embodiments, the positions of the ablationcatheter 104 and the ground catheter 106 described previously may beexchanged.

The system 100 described previously can also be used to create lesionsinside the right atrium. FIG. 31 shows (from outside the heart H) thelocation of the major anatomic landmarks for lesion formation in theright atrium. These landmarks include the superior vena cava (SVC), thetricuspid valve annulus (TVA), the inferior vena cava (IVC), and thecoronary sinus (CS). Tissue nearby these anatomic structures have beenidentified as developing arrhythmia substrates causing atrialfibrillation. Lesions in these tissue regions block reentry paths ordestroy active pacemaker sites and thereby prevent the arrhythmia fromoccurring.

FIGS. 33A to 33C show representative lesion patterns formed inside theright atrium based upon these landmarks. FIG. 33A shows a representativelesion pattern L that extends between the superior vena cava (SVC) andthe tricuspid valve annulus (TVA). The lesion L can be created in aquasi-bipolar manner by directing ablation energy to the ablationcatheter 104 placed at the LA, while the ground catheter 106 is placedinside the LV or the RV. In an alternative embodiment, the positions ofthe ablation catheter 104 and the ground catheter 106 may be exchanged.

FIG. 33B shows a representative lesion pattern that extends between theinterior vena cava (IVC) and the TVA. The lesion L can be created in aquasi-bipolar manner by directing ablation energy to the ablationcatheter 104 placed at the LA, while the ground catheter 106 is placedinside the LV or the RV. In an alternative embodiment, the positions ofthe ablation catheter 104 and the ground catheter 106 may be exchanged.

FIG. 33C shows a representative lesion pattern L that extends betweenthe coronary sinus (CS) and the tricuspid valve annulus (TVA). Thelesion L can be created by directing ablation energy to the ablationcatheter 104 placed at the right atrium (RA), while the ground catheter106 is placed inside the LV, the RV, or the CS. In an alternativeembodiment, the positions of the ablation catheter 104 and the groundcatheter 106 may be exchanged.

Although several examples of lesions that can be created using theabove-described system have been discussed, the above described systemand method can also be used to create lesions at other locations of theheart. For example, in one embodiment, one of the ablation catheter andground catheter 104, 106 can be placed at the atrium at the base of aheart, while the other of the ablation catheter and ground catheter 104,106 is placed at the LV. Such placement of the ablation and groundcatheters 104, 106 allows a lesion to be created at the intersection ofthe atria and the ventricle. In another embodiment, one of the ablationcatheter and ground catheter 104, 106 can be placed at the RV next tothe septum, while the other of the ablation catheter and ground catheter104, 106 is placed at the LV. Such placement of the ablation and groundcatheters 104, 106 allows a lesion to be created at the ventricularseptum. In addition, although the above described system and method havebeen described in the context of cardiac ablation therapy, e.g., fortreating arrhythmias, such as ventricular tachycardia (VT),post-myocardial infraction, atrial fibrillation, supra-VT, flutter, andother heart conditions, it should be understood that the system 100 mayalso be used in many different environments and/or applications. Forexample, the system 100 may also be used to create lesions, such astransmural lesions, at different locations within the body.

Thus, although different embodiments have been shown and described, itwould be apparent to those skilled in the art that many changes andmodifications may be made thereunto without the departing from the scopeof the invention, which is defined by the following claims and theirequivalents.

What is claimed is:
 1. A medical probe, comprising: an elongate memberhaving a proximal end and a distal end; an operative element mounted tothe distal end of the elongate member, the operative element configuredfor conveying or returning ablation energy; an expandable-collapsiblebody surrounding the operative element, wherein theexpandable-collapsible body surrounds the operative element to preventthe operative element from contacting solid tissue, and wherein theexpandable-collapsible body is inflatable and allows the transport ofablation energy from the operative element to outside theexpandable-collapsible body; and an actuatable stabilizer mounted to thedistal end of the elongate member, the stabilizer extending along atleast a portion of an exterior surface of the expandable-collapsiblebody when the expandable-collapsible body is in both an expandedconfiguration and a collapsed configuration.
 2. The medical probe ofclaim 1 wherein the elongate member comprises an inflation lumen havinga distal port distal the distal end of the elongate member.
 3. Themedical probe of claim 2 wherein the elongate member comprises a vacuumlumen having a distal port distal the distal end of the elongate member.4. The medical probe of claim 3 wherein the inflation lumen distal portis longitudinally spaced from the vacuum lumen distal port.
 5. Themedical probe of claim 2 wherein the inflation lumen distal port isdistal the operative element.
 6. The medical probe of claim 2 whereinthe inflation lumen extends through the operative element.
 7. Themedical probe of claim 1 wherein the expandable-collapsible bodycomprises a first layer made from a non-electrically conductivematerial.
 8. The medical probe of claim 7 wherein the pores have adiameter of about 0.1 micrometers.
 9. The medical probe of claim 8,wherein the expandable-collapsible body comprises a second layer, thesecond layer being an electrically conductive layer.
 10. The medicalprobe of claim 9, wherein the expandable-collapsible body has an outersurface and the outer surface has an area, and wherein the electricallyconductive layer has an exposed area of an outwardly facing surface, andwherein the exposed area of the outwardly facing surface of theelectrically conductive layer is less than the area of the outer surfaceof the expandable-collapsible body.
 11. The medical probe of claim 1,wherein the expandable-collapsible body comprises pores in the firstlayer.
 12. The medical probe of claim 11, wherein the inflation lumendistal port faces towards at least some of the pores.
 13. The medicalprobe of claim 1, further comprising a handle assembly secured to aproximal end of the elongate member.
 14. The medical probe of claim 13,wherein the handle assembly comprises a steering mechanism.
 15. Themedical probe of claim 1, wherein the operative element is an electrodeelement configured to provide radiofrequency energy.
 16. The medicalprobe of claim 15, wherein the electrode element surrounds the inflationlumen.
 17. The medical probe of claim 1, wherein theexpandable-collapsible body circumscribes the operative element.
 18. Amethod of treating solid tissue in a body using the medical probe ofclaim 1, comprising: inserting the elongate member into the body toplace the operative element; placing the operative element adjacent thesolid tissue; and maintaining a distance between the operative elementand the solid tissue using the operative element.
 19. The method ofclaim 18, further comprising conveying energy between the operativeelement and the solid tissue, wherein the solid tissue is not ablated bythe operative element.
 20. The medical probe of claim 1, wherein thestabilizer circumscribes at least a portion of the exterior surface ofthe expandable-collapsible body.
 21. The medical probe of claim 1,wherein the stabilizer comprises a material having low electricalconductivity.
 22. The medical probe of claim 1, wherein the stabilizeris vacuum actuatable.